@SteveInOrange
The Deco will determine which connection is best depending on the deman of a connected client, there are no preferences so it is dynamic. The Deco can also use both means of transferring data.
If you look at the power adapter of the Deco P7, the little LED light will tell you if the connection is good. If the light is red then the connection between Decos over powerline is below 50 Mbps. If it is green, then it is above 50 Mbps and the connection is good.
You do not want to place the P7 on a power strip as it can cause interference with the powerline or completely block the communication where it will not work. Similar to how we have recommendations for dedicated powerline devices. You can still do that, in which case the Deco will just rely on the wireless backhaul.